A video showing the Jack-Knives abdominal exercise, a great stomach flattener.
Using a Swiss Ball, place shins on ball & hands on floor in press-up position, keep a natural curve in low back.
Exhale as you contract your abdominals, keeping legs straight, draw legs towards chest, ending with your hips over your head and toes on the ball.
The difficulty can be increased by making the ball smaller, having just one leg on the ball the other suspended, and/or slowing the rep’
An excellent abdominal conditioner, better done as a skill exercise and under control.